Pentagonite is a rare secondary mineral typically found as stunning deep-blue radiating sprays or bow-tie clusters within volcanic vugs. It is chemically dimorphous with its much more common sister mineral, Cavansite, but displays a distinct orthorhombic crystal structure. Collectors prize it for its intense, vibrant color and aesthetic crystal habits, found almost exclusively in the Deccan Traps basalt quarries of India.
Is this pentagonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch pentagonite with a known reference. Pentagonite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Pentagonite leaves a pale blue streak.
- 3Read the lusterHold the specimen under a strong light. Pentagonite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: deep blue, azure blue.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: spray of radiating acicular crystals, bow-tie aggregates.
Often confused with
Pentagonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside pentagonite
Minerals reported to co-occur with pentagonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(V⁴⁺O)Si₄O₁₀·4H₂O
- Mohs hardness
- 3-4
- Density
- 2.33 g/cm³
- Colors
- Streak
- Pale Blue
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Spray of Radiating Acicular Crystals, Bow-tie Aggregates
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Basaltic Vugs in Volcanic Rock
- Typical price
- $20-200 thumbnail, $300-1500+ specimen
Where rockhounds find pentagonite
Classic worldwide localities
- Wagholi Quarry, Pune, India
- Deccan Traps, India
Field-hunting tip
Look in basaltic vugs in volcanic rock country, the host setting where pentagonite typically forms. If you start seeing cavansite, heulandite, stilbite in float, you are in the right ground. Field specimens usually show a spray of radiating acicular crystals, bow-tie aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify pentagonite?+
Where is pentagonite found?+
How much is pentagonite worth?+
What rocks look like pentagonite?+
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Find pentagonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
